block/blk-merge.c

   1 /*
   2  * Functions related to segment and merge handling
   3  */
   4 #include <linux/kernel.h>
   5 #include <linux/module.h>
   6 #include <linux/bio.h>
   7 #include <linux/blkdev.h>
   8 #include <linux/scatterlist.h>
   9
  10 #include "blk.h"
  11
  12 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
  13                                              struct bio *bio,
  14                                              bool no_sg_merge)
  15 {
  16         struct bio_vec bv, bvprv = { NULL };
  17         int cluster, high, highprv = 1;
  18         unsigned int seg_size, nr_phys_segs;
  19         struct bio *fbio, *bbio;
  20         struct bvec_iter iter;
  21
  22         if (!bio)
  23                 return 0;
  24
  25         /*
  26          * This should probably be returning 0, but blk_add_request_payload()
  27          * (Christoph!!!!)
  28          */
  29         if (bio->bi_rw & REQ_DISCARD)
  30                 return 1;
  31
  32         if (bio->bi_rw & REQ_WRITE_SAME)
  33                 return 1;
  34
  35         fbio = bio;
  36         cluster = blk_queue_cluster(q);
  37         seg_size = 0;
  38         nr_phys_segs = 0;
  39         high = 0;
  40         for_each_bio(bio) {
  41                 bio_for_each_segment(bv, bio, iter) {
  42                         /*
  43                          * If SG merging is disabled, each bio vector is
  44                          * a segment
  45                          */
  46                         if (no_sg_merge)
  47                                 goto new_segment;
  48
  49                         /*
  50                          * the trick here is making sure that a high page is
  51                          * never considered part of another segment, since
  52                          * that might change with the bounce page.
  53                          */
  54                         high = page_to_pfn(bv.bv_page) > queue_bounce_pfn(q);
  55                         if (!high && !highprv && cluster) {
  56                                 if (seg_size + bv.bv_len
  57                                     > queue_max_segment_size(q))
  58                                         goto new_segment;
  59                                 if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
  60                                         goto new_segment;
  61                                 if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
  62                                         goto new_segment;
  63
  64                                 seg_size += bv.bv_len;
  65                                 bvprv = bv;
  66                                 continue;
  67                         }
  68 new_segment:
  69                         if (nr_phys_segs == 1 && seg_size >
  70                             fbio->bi_seg_front_size)
  71                                 fbio->bi_seg_front_size = seg_size;
  72
  73                         nr_phys_segs++;
  74                         bvprv = bv;
  75                         seg_size = bv.bv_len;
  76                         highprv = high;
  77                 }
  78                 bbio = bio;
  79         }
  80
  81         if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
  82                 fbio->bi_seg_front_size = seg_size;
  83         if (seg_size > bbio->bi_seg_back_size)
  84                 bbio->bi_seg_back_size = seg_size;
  85
  86         return nr_phys_segs;
  87 }
  88
  89 void blk_recalc_rq_segments(struct request *rq)
  90 {
  91         bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
  92                         &rq->q->queue_flags);
  93
  94         rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
  95                         no_sg_merge);
  96 }
  97
  98 void blk_recount_segments(struct request_queue *q, struct bio *bio)
  99 {
 100         if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
 101                         bio->bi_vcnt < queue_max_segments(q))
 102                 bio->bi_phys_segments = bio->bi_vcnt;
 103         else {
 104                 struct bio *nxt = bio->bi_next;
 105
 106                 bio->bi_next = NULL;
 107                 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
 108                 bio->bi_next = nxt;
 109         }
 110
 111         bio->bi_flags |= (1 << BIO_SEG_VALID);
 112 }
 113 EXPORT_SYMBOL(blk_recount_segments);
 114
 115 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 116                                    struct bio *nxt)
 117 {
 118         struct bio_vec end_bv = { NULL }, nxt_bv;
 119         struct bvec_iter iter;
 120
 121         if (!blk_queue_cluster(q))
 122                 return 0;
 123
 124         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
 125             queue_max_segment_size(q))
 126                 return 0;
 127
 128         if (!bio_has_data(bio))
 129                 return 1;
 130
 131         bio_for_each_segment(end_bv, bio, iter)
 132                 if (end_bv.bv_len == iter.bi_size)
 133                         break;
 134
 135         nxt_bv = bio_iovec(nxt);
 136
 137         if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
 138                 return 0;
 139
 140         /*
 141          * bio and nxt are contiguous in memory; check if the queue allows
 142          * these two to be merged into one
 143          */
 144         if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
 145                 return 1;
 146
 147         return 0;
 148 }
 149
 150 static inline void
 151 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 152                      struct scatterlist *sglist, struct bio_vec *bvprv,
 153                      struct scatterlist **sg, int *nsegs, int *cluster)
 154 {
 155
 156         int nbytes = bvec->bv_len;
 157
 158         if (*sg && *cluster) {
 159                 if ((*sg)->length + nbytes > queue_max_segment_size(q))
 160                         goto new_segment;
 161
 162                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
 163                         goto new_segment;
 164                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
 165                         goto new_segment;
 166
 167                 (*sg)->length += nbytes;
 168         } else {
 169 new_segment:
 170                 if (!*sg)
 171                         *sg = sglist;
 172                 else {
 173                         /*
 174                          * If the driver previously mapped a shorter
 175                          * list, we could see a termination bit
 176                          * prematurely unless it fully inits the sg
 177                          * table on each mapping. We KNOW that there
 178                          * must be more entries here or the driver
 179                          * would be buggy, so force clear the
 180                          * termination bit to avoid doing a full
 181                          * sg_init_table() in drivers for each command.
 182                          */
 183                         sg_unmark_end(*sg);
 184                         *sg = sg_next(*sg);
 185                 }
 186
 187                 sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
 188                 (*nsegs)++;
 189         }
 190         *bvprv = *bvec;
 191 }
 192
 193 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
 194                              struct scatterlist *sglist,
 195                              struct scatterlist **sg)
 196 {
 197         struct bio_vec bvec, bvprv = { NULL };
 198         struct bvec_iter iter;
 199         int nsegs, cluster;
 200
 201         nsegs = 0;
 202         cluster = blk_queue_cluster(q);
 203
 204         if (bio->bi_rw & REQ_DISCARD) {
 205                 /*
 206                  * This is a hack - drivers should be neither modifying the
 207                  * biovec, nor relying on bi_vcnt - but because of
 208                  * blk_add_request_payload(), a discard bio may or may not have
 209                  * a payload we need to set up here (thank you Christoph) and
 210                  * bi_vcnt is really the only way of telling if we need to.
 211                  */
 212
 213                 if (bio->bi_vcnt)
 214                         goto single_segment;
 215
 216                 return 0;
 217         }
 218
 219         if (bio->bi_rw & REQ_WRITE_SAME) {
 220 single_segment:
 221                 *sg = sglist;
 222                 bvec = bio_iovec(bio);
 223                 sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
 224                 return 1;
 225         }
 226
 227         for_each_bio(bio)
 228                 bio_for_each_segment(bvec, bio, iter)
 229                         __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
 230                                              &nsegs, &cluster);
 231
 232         return nsegs;
 233 }
 234
 235 /*
 236  * map a request to scatterlist, return number of sg entries setup. Caller
 237  * must make sure sg can hold rq->nr_phys_segments entries
 238  */
 239 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 240                   struct scatterlist *sglist)
 241 {
 242         struct scatterlist *sg = NULL;
 243         int nsegs = 0;
 244
 245         if (rq->bio)
 246                 nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
 247
 248         if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
 249             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
 250                 unsigned int pad_len =
 251                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
 252
 253                 sg->length += pad_len;
 254                 rq->extra_len += pad_len;
 255         }
 256
 257         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
 258                 if (rq->cmd_flags & REQ_WRITE)
 259                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
 260
 261                 sg->page_link &= ~0x02;
 262                 sg = sg_next(sg);
 263                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
 264                             q->dma_drain_size,
 265                             ((unsigned long)q->dma_drain_buffer) &
 266                             (PAGE_SIZE - 1));
 267                 nsegs++;
 268                 rq->extra_len += q->dma_drain_size;
 269         }
 270
 271         if (sg)
 272                 sg_mark_end(sg);
 273
 274         return nsegs;
 275 }
 276 EXPORT_SYMBOL(blk_rq_map_sg);
 277
 278 /**
 279  * blk_bio_map_sg - map a bio to a scatterlist
 280  * @q: request_queue in question
 281  * @bio: bio being mapped
 282  * @sglist: scatterlist being mapped
 283  *
 284  * Note:
 285  *    Caller must make sure sg can hold bio->bi_phys_segments entries
 286  *
 287  * Will return the number of sg entries setup
 288  */
 289 int blk_bio_map_sg(struct request_queue *q, struct bio *bio,
 290                    struct scatterlist *sglist)
 291 {
 292         struct scatterlist *sg = NULL;
 293         int nsegs;
 294         struct bio *next = bio->bi_next;
 295         bio->bi_next = NULL;
 296
 297         nsegs = __blk_bios_map_sg(q, bio, sglist, &sg);
 298         bio->bi_next = next;
 299         if (sg)
 300                 sg_mark_end(sg);
 301
 302         BUG_ON(bio->bi_phys_segments && nsegs > bio->bi_phys_segments);
 303         return nsegs;
 304 }
 305 EXPORT_SYMBOL(blk_bio_map_sg);
 306
 307 static inline int ll_new_hw_segment(struct request_queue *q,
 308                                     struct request *req,
 309                                     struct bio *bio)
 310 {
 311         int nr_phys_segs = bio_phys_segments(q, bio);
 312
 313         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
 314                 goto no_merge;
 315
 316         if (bio_integrity(bio) && blk_integrity_merge_bio(q, req, bio))
 317                 goto no_merge;
 318
 319         /*
 320          * This will form the start of a new hw segment.  Bump both
 321          * counters.
 322          */
 323         req->nr_phys_segments += nr_phys_segs;
 324         return 1;
 325
 326 no_merge:
 327         req->cmd_flags |= REQ_NOMERGE;
 328         if (req == q->last_merge)
 329                 q->last_merge = NULL;
 330         return 0;
 331 }
 332
 333 int ll_back_merge_fn(struct request_queue *q, struct request *req,
 334                      struct bio *bio)
 335 {
 336         if (blk_rq_sectors(req) + bio_sectors(bio) >
 337             blk_rq_get_max_sectors(req)) {
 338                 req->cmd_flags |= REQ_NOMERGE;
 339                 if (req == q->last_merge)
 340                         q->last_merge = NULL;
 341                 return 0;
 342         }
 343         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
 344                 blk_recount_segments(q, req->biotail);
 345         if (!bio_flagged(bio, BIO_SEG_VALID))
 346                 blk_recount_segments(q, bio);
 347
 348         return ll_new_hw_segment(q, req, bio);
 349 }
 350
 351 int ll_front_merge_fn(struct request_queue *q, struct request *req,
 352                       struct bio *bio)
 353 {
 354         if (blk_rq_sectors(req) + bio_sectors(bio) >
 355             blk_rq_get_max_sectors(req)) {
 356                 req->cmd_flags |= REQ_NOMERGE;
 357                 if (req == q->last_merge)
 358                         q->last_merge = NULL;
 359                 return 0;
 360         }
 361         if (!bio_flagged(bio, BIO_SEG_VALID))
 362                 blk_recount_segments(q, bio);
 363         if (!bio_flagged(req->bio, BIO_SEG_VALID))
 364                 blk_recount_segments(q, req->bio);
 365
 366         return ll_new_hw_segment(q, req, bio);
 367 }
 368
 369 /*
 370  * blk-mq uses req->special to carry normal driver per-request payload, it
 371  * does not indicate a prepared command that we cannot merge with.
 372  */
 373 static bool req_no_special_merge(struct request *req)
 374 {
 375         struct request_queue *q = req->q;
 376
 377         return !q->mq_ops && req->special;
 378 }
 379
 380 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
 381                                 struct request *next)
 382 {
 383         int total_phys_segments;
 384         unsigned int seg_size =
 385                 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
 386
 387         /*
 388          * First check if the either of the requests are re-queued
 389          * requests.  Can't merge them if they are.
 390          */
 391         if (req_no_special_merge(req) || req_no_special_merge(next))
 392                 return 0;
 393
 394         /*
 395          * Will it become too large?
 396          */
 397         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
 398             blk_rq_get_max_sectors(req))
 399                 return 0;
 400
 401         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
 402         if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
 403                 if (req->nr_phys_segments == 1)
 404                         req->bio->bi_seg_front_size = seg_size;
 405                 if (next->nr_phys_segments == 1)
 406                         next->biotail->bi_seg_back_size = seg_size;
 407                 total_phys_segments--;
 408         }
 409
 410         if (total_phys_segments > queue_max_segments(q))
 411                 return 0;
 412
 413         if (blk_integrity_rq(req) && blk_integrity_merge_rq(q, req, next))
 414                 return 0;
 415
 416         /* Merge is OK... */
 417         req->nr_phys_segments = total_phys_segments;
 418         return 1;
 419 }
 420
 421 /**
 422  * blk_rq_set_mixed_merge - mark a request as mixed merge
 423  * @rq: request to mark as mixed merge
 424  *
 425  * Description:
 426  *     @rq is about to be mixed merged.  Make sure the attributes
 427  *     which can be mixed are set in each bio and mark @rq as mixed
 428  *     merged.
 429  */
 430 void blk_rq_set_mixed_merge(struct request *rq)
 431 {
 432         unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
 433         struct bio *bio;
 434
 435         if (rq->cmd_flags & REQ_MIXED_MERGE)
 436                 return;
 437
 438         /*
 439          * @rq will no longer represent mixable attributes for all the
 440          * contained bios.  It will just track those of the first one.
 441          * Distributes the attributs to each bio.
 442          */
 443         for (bio = rq->bio; bio; bio = bio->bi_next) {
 444                 WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) &&
 445                              (bio->bi_rw & REQ_FAILFAST_MASK) != ff);
 446                 bio->bi_rw |= ff;
 447         }
 448         rq->cmd_flags |= REQ_MIXED_MERGE;
 449 }
 450
 451 static void blk_account_io_merge(struct request *req)
 452 {
 453         if (blk_do_io_stat(req)) {
 454                 struct hd_struct *part;
 455                 int cpu;
 456
 457                 cpu = part_stat_lock();
 458                 part = req->part;
 459
 460                 part_round_stats(cpu, part);
 461                 part_dec_in_flight(part, rq_data_dir(req));
 462
 463                 hd_struct_put(part);
 464                 part_stat_unlock();
 465         }
 466 }
 467
 468 /*
 469  * Has to be called with the request spinlock acquired
 470  */
 471 static int attempt_merge(struct request_queue *q, struct request *req,
 472                           struct request *next)
 473 {
 474         if (!rq_mergeable(req) || !rq_mergeable(next))
 475                 return 0;
 476
 477         if (!blk_check_merge_flags(req->cmd_flags, next->cmd_flags))
 478                 return 0;
 479
 480         /*
 481          * not contiguous
 482          */
 483         if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
 484                 return 0;
 485
 486         if (rq_data_dir(req) != rq_data_dir(next)
 487             || req->rq_disk != next->rq_disk
 488             || req_no_special_merge(next))
 489                 return 0;
 490
 491         if (req->cmd_flags & REQ_WRITE_SAME &&
 492             !blk_write_same_mergeable(req->bio, next->bio))
 493                 return 0;
 494
 495         /*
 496          * If we are allowed to merge, then append bio list
 497          * from next to rq and release next. merge_requests_fn
 498          * will have updated segment counts, update sector
 499          * counts here.
 500          */
 501         if (!ll_merge_requests_fn(q, req, next))
 502                 return 0;
 503
 504         /*
 505          * If failfast settings disagree or any of the two is already
 506          * a mixed merge, mark both as mixed before proceeding.  This
 507          * makes sure that all involved bios have mixable attributes
 508          * set properly.
 509          */
 510         if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
 511             (req->cmd_flags & REQ_FAILFAST_MASK) !=
 512             (next->cmd_flags & REQ_FAILFAST_MASK)) {
 513                 blk_rq_set_mixed_merge(req);
 514                 blk_rq_set_mixed_merge(next);
 515         }
 516
 517         /*
 518          * At this point we have either done a back merge
 519          * or front merge. We need the smaller start_time of
 520          * the merged requests to be the current request
 521          * for accounting purposes.
 522          */
 523         if (time_after(req->start_time, next->start_time))
 524                 req->start_time = next->start_time;
 525
 526         req->biotail->bi_next = next->bio;
 527         req->biotail = next->biotail;
 528
 529         req->__data_len += blk_rq_bytes(next);
 530
 531         elv_merge_requests(q, req, next);
 532
 533         /*
 534          * 'next' is going away, so update stats accordingly
 535          */
 536         blk_account_io_merge(next);
 537
 538         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 539         if (blk_rq_cpu_valid(next))
 540                 req->cpu = next->cpu;
 541
 542         /* owner-ship of bio passed from next to req */
 543         next->bio = NULL;
 544         __blk_put_request(q, next);
 545         return 1;
 546 }
 547
 548 int attempt_back_merge(struct request_queue *q, struct request *rq)
 549 {
 550         struct request *next = elv_latter_request(q, rq);
 551
 552         if (next)
 553                 return attempt_merge(q, rq, next);
 554
 555         return 0;
 556 }
 557
 558 int attempt_front_merge(struct request_queue *q, struct request *rq)
 559 {
 560         struct request *prev = elv_former_request(q, rq);
 561
 562         if (prev)
 563                 return attempt_merge(q, prev, rq);
 564
 565         return 0;
 566 }
 567
 568 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 569                           struct request *next)
 570 {
 571         return attempt_merge(q, rq, next);
 572 }
 573
 574 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 575 {
 576         struct request_queue *q = rq->q;
 577
 578         if (!rq_mergeable(rq) || !bio_mergeable(bio))
 579                 return false;
 580
 581         if (!blk_check_merge_flags(rq->cmd_flags, bio->bi_rw))
 582                 return false;
 583
 584         /* different data direction or already started, don't merge */
 585         if (bio_data_dir(bio) != rq_data_dir(rq))
 586                 return false;
 587
 588         /* must be same device and not a special request */
 589         if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
 590                 return false;
 591
 592         /* only merge integrity protected bio into ditto rq */
 593         if (bio_integrity(bio) != blk_integrity_rq(rq))
 594                 return false;
 595
 596         /* must be using the same buffer */
 597         if (rq->cmd_flags & REQ_WRITE_SAME &&
 598             !blk_write_same_mergeable(rq->bio, bio))
 599                 return false;
 600
 601         if (q->queue_flags & (1 << QUEUE_FLAG_SG_GAPS)) {
 602                 struct bio_vec *bprev;
 603
 604                 bprev = &rq->biotail->bi_io_vec[bio->bi_vcnt - 1];
 605                 if (bvec_gap_to_prev(bprev, bio->bi_io_vec[0].bv_offset))
 606                         return false;
 607         }
 608
 609         return true;
 610 }
 611
 612 int blk_try_merge(struct request *rq, struct bio *bio)
 613 {
 614         if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 615                 return ELEVATOR_BACK_MERGE;
 616         else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 617                 return ELEVATOR_FRONT_MERGE;
 618         return ELEVATOR_NO_MERGE;
 619 }